Abu Hurairah reported to the Messenger of Allah( may peace be upon him) as sayings:
People will continue to ask one another(questions) till this is pronounced: Allah created all things, but who created Allah ? Whoever comes across anything of that, he should say: I believe in Allah.

حَدَّثَنَا هَارُونُ بْنُ مَعْرُوفٍ، حَدَّثَنَا سُفْيَانُ، عَنْ هِشَامٍ، عَنْ أَبِيهِ، عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ ﷺ " لاَ يَزَالُ النَّاسُ يَتَسَاءَلُونَ حَتَّى يُقَالَ هَذَا خَلَقَ اللَّهُ الْخَلْقَ فَمَنْ خَلَقَ اللَّهَ فَمَنْ وَجَدَ مِنْ ذَلِكَ شَيْئًا فَلْيَقُلْ آمَنْتُ بِاللَّهِ " .